Catalytic alkylation of iso-paraffin with olefins



W'. W. GARY Oct. 7, 1947.

CATALYTIC ALKYLATION OF ISO#PARAFFIN WITH O`LEFINS Filed NOV. 26, 1941.

Nw v MU NJ wR-IGHT w. GARY INVENTOR i BY e? ATTORN EYS Patented Oct. 7,1%?47 CATALY'IIC ALKYLATION OF ISO-PARAFFIN WITH OLEFIN S l/Vright W.Gary, Los Angeles, Calif., assigner to The M. W. Kellogg Company, JerseyCity, N. J., a corporation of Delaware Application November 26, 1941,Serial No. 420,511

7 Claims. (Cl. 26o-683.4)

This invention relates to the alkylation of isobutane with butylene inthe presence of a catalyst, and more particularly to the preparation ofmixtures of the latter hydrocarbons in their alkylate-formingproportions from certain random mixtures of the various isoand normal C4parafns and olefins.

As is well known, a high octane aviation fuel blending stock may beobtained by alkylating isobutane with butylene in the presence ofcatalysts of the sulfuric acid type. In this reaction each mol ofiso-butane apparently reacts with one mol of butylene, so that ideallythe feed to the process should contain the iso-paraihn and olen inequi-molal proportions. In practice, however, it is customary to obtainfeed stocks for alkylation from natural gas and gasoline, refineryresidue gases produced in oil cracking operations, and other sources inwhich not only is there rarely the ideal iso-parafn/olefin ratio, butwhich almost invariably contain the non-alkylatable hydrocarbon, normalbutane.

In many cases, of course, it is possible to combine C4 fractions fromdiiferent sources and hav-Y ing different iso-paranin/'olen ratios toobtain an approximate balance. In numerous other cases, however, andmost frequently when all the materials must be obtained from a singlesource, gross disparities in the available quantities of isobutane andbutylene are met with.

One of the objects of the present invention is to provide a method ofpreparing a feed stock for alkylation having a balancediso-butane/butylene ratio from a mixture of C4 hydrocarbons whereinthere is a deficiency of butylene.

Another object of the invention is to provide a process whereby analkylation feed stock may be prepared from normal butano. Other objectsand advantages of the invention will appear during the course of thedescription hereinafter given.

In order to achieve the above and related ends it is contemplated by theinvention to convert -normal butane into iso-butane by catalyticisomerization, and then to convert iso-butane into butylene bynon-catalytic pyrolysis, or what might be called purely thermaldehydrogenation. I have found that whereas at best a yield of -butyleneof only 20 to 25 per cent is obtainable in pyrolyzing normal butane,iso-butano may be thermally dehydrogenate'd to yield as much as 60 percent of butylene. The combination of an isomerization step with apyrolysis step thus affords a route whereby butylene deficiencies maybe` made up at the expense of the normal b-utane, 55

2 which otherwise could not be used efficiently for the production ofalkylate.

In the event that the quantity of butylene obtainable from normal butanein accordance with the invention is still not suiilcient to effect aniso-butane/butylene balance when combined with alkylation reactantsalready available, I may subject a sufficient quantity of the excessiso-butane to pyrolysis along with the iso-butane obtained from normalbutano, and thereby correct even the most disparate iso-butane/butyleneratios. If on the other hand there is more than enough normal butane toproduce the butylene required to balance the available quantity ofiso-butano, I may withhold from the pyrolysis step a portion of theiso-butane produced by isomerization, the Withheld portion being 0Isuillcient sizev to bring into balance the nal overalliso-butane/butylene ratio,

An exemplary embodiment of the invention will now be described in detailand suitable conditions of operation will be given for the severalconversion stages involved, the description being with reference to theannexed drawing. The drawing is a schematic flow sheet wherein unitaryprocessing stages are conventionally designated for greater clarity byrectangular blocks bearing identifying legends.

In the drawing, the alkylation step 2 comprises conventional catalyticiso-butane-butylene alkylation in the presence of a catalyst such as 96%sulfuric acid, followed by fractionation of the product into alkylateand unreacted isobutane and normal butane. The presence of unreactediso-butane in the alkylation product arises from the fact that thealkylation reaction is preferably carried out with about 5 to 8 mols `ofiso-butane present per mol of butylene. The

excess iso-butane influences the course of the alkylation reactionWithout actually taking part in it, and is Withdrawn unchanged in theproduct mixture. After being separated from the alkylate and from normalbutane this excess iso-butane, or an equivalent amount taken from someother source, must be returned to the alkylation zone to maintain thedesired iso-butane/olen ratio therein. 'Ihe latter ratio is not to beconfused with the 1:1 ratio in which the two reactants actually combine.

The isomerization step 6 is likewise a conventional operation comprisingthe contacting of normal butane with a suitable catalyst such asaluminum chloride. I prefer to employ with the latter catalyst anisomerization temperature between about F. and 250 F. and a pressure Ynarily from about 40 to about 75 per cent of normal butane, 'dependingupon the time of Contact with the catalyst. In View of the practicalabsence of side-reactions, however, it becomes possible to obtain anultimate yield of iso-butane of Y substantially 100 per cent byreturning unreactcd normal butane for further contacting wi'tl'rtlfieVcatalyst. As will be hereinafter explained, com'- plete conversion ofnormal butane to iso-butane is accomplished in accordance with theinvention." i

For purposes of illustration, however, it will be assumed that thepartially vconverted mixture obtained from the isomerization step 6contains 40 per cent iso-butane and 60 per cent normal butane.

The pyrolysis step 9 is accomplished by heating iso-butane, suitably ina pipe coil or conventional tubular furnace, to approximately 1000 F. to1100" F., and maintaining it at the elevated tenihr perature for a briefperiod.

The yield of butylene which Will be obtained by this pyrolysis ischiefly determined by the operating pressure and by the length of timethat the reactant material is maintainedat the conversion temperature.The highest ultimate yields, ranging up to 60 per cent or better, areobtained at atmospheric pressure and with a relatively short conversiontime. In order to rec'iluce` the requisite furnace tube volume,-however, it will usually be more economical to employ a pres- 'sure of100 to 200 pounds per square inch. The pyrolysis reaction is like theisomerization reaction in that complete conversion is not effected in asingle pass through the conversion zone. It is unlike the isomerizationreaction in that side-reactions result in the formation of appreciablequantities of C3 and lighter hydrocarbons. The pyrolysis step 9 shown inthe drawing includ'es removal of the light by-products from the productbutylene and unconverted iso`butane, but not the separation of thelatter two confstituents. The highest ultimate yields of butylene areobtained in a short time, high recycle ratio Operation wherein the yieldper pass is relatively low; 20 per cent per pass is a suitable figureand will be assumed herein for illustrative purposes. l

An ultimate yield of butylene of approximately 50 per cent is readilyobtainable in the pyrolysis step and will be assumed for the purpose ofthe present example. The return of unconverted isobutane 'to thepyrolysis step is indirect and will be understood from the descriptionhereinafter givenl Y I't will be assumed further for illustrative purposes in the example hereinafter described that a mixture of C4hydrocarbons, such as might be separated from the byeproduct gasproduced in cracking petroleum oils, is available as the net alkylationfeed stock and that therelative proportions of the C4 hydrocarbons areas follows: Normal butane, 5-0 mols; iso-butane, v3U mols; and butylene,mols; total, 100 mols.

In the drawing, the above described or mixture is supplied to alkylationprocess 2 as indicated by line i; there is simultaneously supplied tothe process 50 mols of iso-butane and "75 mols of vnormalV butanethrough line '8,' and 20 .mols of f butylene and 60 mols of iso-butanethrough line i2. Also,`100 mols of iso-butane are supplied through lineIl. The gross feed therefore consists of iso-butane, 240 mols; butylene,40 mols; and normal butane, 125 mols; total, 405 mols.

In the alkylation reactor, the 40 mols of butylene react with 40 mols ofiso-butane to form alkylate, leaving200 mols of iso-butane and 125 molsof normal butane unreacted. The alkylate is separated by fractionationand disposed of as desired, as indicated by line 3.

The 12.5 mols of normal butane are likewise separated and transferredvia line l to the isom- Verization step, wherein 50 mols (40 per cent)thereof are converted into iso-butane. VThe isomerization product,consisting of this 50 mols of iso-butane plus the remaining mols ofnormal butane, is returned via line 8 to the alkylation reactor to makeup a portion of the gross feed thereto.

The 200 mols of iso-butane in the alkylation Vproduct is separated byfractionation andafter withdrawal as indicated by line 5 is subdividedinto two portions. The first, consisting of mols, is returnedimmediately to 'the alkylati'on process via line il to maintain thedesiredisobutane/butylene ratio of 6:1 (240 mols iso-butane/40 molsbutylene) in the alkylation Vrzone.

The second portion of 100 mols is transferred as indicated by line i0 tothe pyrolysis step wherea in, in one pass, yields of 20 mols of butyleneand 20 mols of light gaseous by-products are obrt'ai'ned by theconversion of 40 mols vof the iso-r butane, 60 mols remainingunaffected. After separation and disposal of the by-p'roducts throughline l, the mixture of 60 mols ofV isoa butane and v20 mols of butylenerisreturned as indicated by line l2 to the alkylation step. 4

It will be seen that the quantities of materials charged to theindividual steps and to the combined system are in balance with theintermediate and nal products. It will also be seen that in thisembodiment of the invention, the recycling of unconverted normal butaneand iso-butane to 'the isomeriz'ation and pyrolysis steps, respectively,is by way of the alkylation step, wherein removal of the respective'conversion products'is effected through the agency of the alkylationreaction. Although I prefer to accomplish recycling in this way, it willbe understood by those skilled in the art that, if desired, pureiso-butane and butylene could be returned to the alk'ylation stepthrough lines 8, and I2 respectively, instead of partially convertedmixtures, by vaugmenting the isomerization and pyrolysis rsteps eachwith rits own individual fractionation system, whereby unconvertedmaterial could be separated for immediate recycling. In the latter eventthe'quantity of iso-butane recycled through lines 5 and rIl for thebenefit of the alkylation reaction would need to be increased, becauseof the absence of any iso-butane recycle in the butylene returne'c'll 75mols of iso-butane in the net feed, and a portion of the iso-butane inthe net feed would have had to be sent to the pyrolysis step. If on theother hand there had been more than the assumed amount of butylene inthe feed stock, a smaller proportion of the total available isobutanewould have been pyrolyzed.

My invention is not limited by any of the illustrative examples herein,but only by the following claims.

I claim:

1. The method of preparing a high octane motor fuel from normal butanewhich comprises catalytically isomerizing normal butane to formiso-butane, pyrolyzing a portion of the thusproduced iso-butane toproduce butylene, and catalytically alkylating thus-produced butylenewith iso-butane produced in said isomerization step.

2. A method of preparing a high octane motor fuel from a mixture ofiso-butane, normal butane and butylene, wherein there is less than anequimolal proportion of butylene relative to the isobutane, whichcomprises adding butylene to the mixture and then subjecting the mixtureto catalytic Ibutylene-iso-butane alkylation, separating normal butanefrom the alkylation product and converting thus-separated normal butaneinto iso-butane by catalytic isomerization, pyrolyzing thus-producediso-butane to produce butylene, adding thus-produced butylene to furtherquantities of said mixture to be alkylated as aforesaid, and repeatingsaid sequence of steps.

3. A method of preparing a high octane motor fuel from a mixture ofisoand normal butane and butylene which comprises introducing saidmixture into a catalytic alkylation zone, simultaneously introducinginto said zone a second mixture consisting of normal and iso-butane anda third mixture consisting of iso-butane and butylene, catalyticallyalkylating iso-butane with butylene in said Zone, withdrawing a productmixture of alkylate, iso-butane, and normal butane from said zone andfractionally distilling it to separate isoand normal butane fromalkylate land from each other, contacting the thus-separated normalbutane with an isomerization catalyst to form a mixture of normal andisobutane, returning said last-mentioned mixture to said alkylation zoneas said second mixture aforesaid, subjecting iso-butane separated fromsaid product mixture to pyrolysis to convert it partially into butyleneand lighter by-products, separating said by-products from butylene anduncoverted iso-butane, and returning a mixture of said latter twomaterials to said alkylation zone as said third mixture aforesaid.

4. In a process for alkylating iso-butane wit butylene in an alkylationstep in which iso- .butane is maintained in substantial excess overbutylene in a liquid acid catalyst alkylation zone and the reactionproducts are fractionated to separate an iso-butane fraction and anormal butane fraction, the improvement which comprises subjecting atleast a portion of said isobutane fraction to thermal dehydrogenation ina pyrolysis step, recycling any remainder of said iso-butane fraction tosaid alkylation reaction zone, conducting said thermal dehydrogenationtreatment under conditions of temperature and reaction time effective toconvert a substantial proportion of the iso-butane to butylene whileminimizing the formation of other products, re-

cycling to said alkylation step butylene obtained as a product of saidthermal dehydrogenation treatment, subjecting at least a portion of saidnormal butane fraction to catalytic isomerization treatment to effectconversion thereof to isobutane, and recycling the isomerization productto said alkylation step.

5. In a process for alkylating iso-butane with butylene in an alkylationstep in which iso-butane is maintained in substantial excess overbutylene in a liquid acid catalyst alkylation zone and the reactionproducts are fractionated to separate an iso-butane fraction and anormal butane fraction, the improvement which comp-rises subjecting atleast a portion of said iso-butane fraction to thermal dehydrogenationin a pyrolysis step, recycling any remainder of said iso-butane fractionto said alkylation reaction zone, conducting said thermaldehydrogenation treatment under conditions of temperature and reactiontime effective to convert a substantial proportion of the isobutane tobutylene while minimizing the formation of other products, recycling tosaid alkylation step butylene obtained as a product of said thermaldehydrogenation treatment, subjecting at least a portion of said normalbutane fraction to catalytic isomerization treatment to effect conversion thereof to iso-butane, and recycling to said alkylation step amixture of normal butane and iso-butane obtained as a product of saidisomerization treatment.

6. The method of preparing a high octane motor fuel which comprisescatalytically isomerizing normal butane to form iso-butane, pyrolyzingat least a portion of the iso-butane thus obtained to produce butylene,and catalytically reacting butylene thus obtained with isobutane toproduce a motor fuel ingredient of high anti-kno ck value.

7. The method of preparing a high octane motor fuel which comprisespyrolyzing iso-butane to produce butylene, catalytically isomerizingnormal butane to form iso-butane and catalytically alkylating butylenethus obtained with isobutane produced in said isomerization step.

WRIGHT W. GARY.

REFERENCES CITED Ihe following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,069,624 Prutton et al Feb. 2,1937 2,276,171 Ewell Mar. 10, 1942 2,303,663 Shankland Deo. 1, 1942OTHER REFERENCES The Reactions of Pure Hydrocarbons, by Egloff, ReinholdPub. Co., New York, N. Y., 1937, pages 147 to 165. (Copy in Division31.)

